1. Field of the Invention
The present invention relates to improvements in a homokinetic transmission joint for motor vehicles.
2. Description of the Prior Art
A homokinetic transmission joint is known which is partly represented in the accompanying FIG. 1 and comprises a male element capable of being driven in rotation by a driving shaft AM and provided with radial arms or trunnions 340, for example three trunnions forming a tripod. Mounted on each arm 340 is a rolling element constituted by two separate sectors of which only sector 310 has been shown in FIG. 1, these sectors each cooperating with a rolling track R formed in a female element (barrel 312) connected to rotate with a driven shaft (not shown).
Elastic expansible bearing bushings are interposed between the arms 340 and the rolling sectors 310, each bushing 320 being formed by two cylindrical semi-bushings 320A and 320B each provided with a curved end edge 330 constituting an anchoring point engaged in an aperture formed radially in the arm 340. The semi-bushings 320A, 320B are elastic and adapted to be capable of radially expanding by a pinching of the associated arm 340 between their ends.
The aperture machined in the arm 340 receiving the anchoring point constituted by the curved edge 330 is angularly offset 90.degree. relative to the mean direction Y--Y' of the load P applied on the bushing 320. Now, in the case where the angularity of the joint is maximum, when the rolling segment 310 journalled on the bushing 320 is in its extreme position and starts its return travel, the force P is shifted to P' and the bushing 320 is uncovered on an arc .alpha. exceeding 90.degree.. A frictional force F then appears at the point 500 located at the intersection between the inner surface of the rolling segment 310 and the corresponding semi-bushing 320B. This force F tends to drive the semi-bushing 320B in rotation and causes the creation of a reaction force Q applied on the indexing end edge 330.
With l being the distance between the point 500 and the point of application of the reaction force Q, there results a bending moment Ql at the point 500 in the semi-bushing 320B which bends by modifying its curvature in its zone of entry under the segment 310. This modification of curvature increases in an exaggerated manner the local pressure in this zone 500 and destroys the film of lubricant, which results in a start of seizure between the segment 310 and the semi-bushing 320B. Correlatively, the force retaining the indexing end 330 suddenly increases, as does the bending, which may result in the fracture of the semi-bushing 320B at the point 500.